Specific dye compound, optical information recording medium comprising specific dye, and information recording method using this optical information recording medium

ABSTRACT

The present invention provides an optical information recording medium comprising a substrate having disposed thereon a recording layer, wherein the recording layer includes a recording dye represented by the following formula (I) or (II): 
     
       
         
         
             
             
         
       
         
         
           
             wherein A represents an aromatic ring which may have a substituent, B represents an aromatic ring which may have a substituent other than a hydroxyl group, n is an integer of 1 to 3, m is an integer of 2 to 6, L represents a bivalent linking group, which may have a substituent, or a single bond, and V represents an aromatic ring, which may have a substituent other than L.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplication No. 2003-171795, the disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information recordingmedium, to an information recording method capable of recording andreproducing information by using a laser, and to a dye compound. Inparticular, the invention relates to a heat mode type opticalinformation recording medium, to an information recording methodsuitable for recording information by using a short wavelength laserhaving a wavelength of 440 nm or less, and to a dye compound.

2. Description of the Related Art

An optical information recording medium (optical disc) capable ofrecording information only once by using a laser has been conventionallyknown. This disc is called a write-once type CD (the so-called CD-R).The disc typically has a structure in which a recording layer made of anorganic dye, a light-reflective layer made of a metal such as gold and aprotective layer made of a resin are laminated on a transparent discsubstrate in that order. Information is recorded on the CD-R byradiating onto the CD-R near infrared ray laser beams, which usuallyhave a wavelength of around 780 nm. Specifically, the laser-radiatedportions of the recording layer absorb the light, so that thetemperature of the portions rises locally. Consequently, the physical orchemical properties of the portions change (for example, generation ofpits), and information is recorded as a result of the optical propertiesof the portions being changed.

Meanwhile, the information is read (reproduced) by radiating onto therecording layer laser beams having the same wavelength as those of therecording laser beams. Specifically, information is reproduced bydetecting the difference between reflectivity of portions of therecording layer having a changed optical property (recorded portions)and reflectivity of portions of the recording layer having an unchangedoptical property (non-recorded portions).

In recent years, optical information recording media having a higherrecording density have been demanded. To meet such a demand, an opticaldisc called a recordable digital versatile disc (the so-called DVD-R)has appeared on the market (“Nikkei New Media”, special edition “DVD”,published in 1995). This DVD-R has a structure in which two discs eachhaving a recording layer made of a dye, a light-reflective layer whichis usually formed on the recording layer, and, if necessary, aprotective layer on a transparent disc-shaped substrate having a guidegroove (a pre-groove) which is tracked with radiated laser beams andwhose width (i.e., 0.74 to 0.8 μm) is half or less of the width ofgrooves in CD-Rs, are bonded to each other with an adhesive so that therecording layer is disposed inside the DVD-R. Alternatively, the DVD-Rhas a structure in which the disc and a protective substrate having thesame shape as the disc are bonded to each other with an adhesive so thatthe recording layer is disposed inside. The recording and reproducing ofinformation in this DVD-R are performed by radiating onto the DVD-Rvisible laser beams, which usually have a wavelength of 630 to 680 nm.In the DVD-R, recordings of higher density can be attained than in theCD-R.

Recently, networks such as the Internet, and high-vision TV have beenexpanding rapidly. Moreover, the days of broadcasting by high definitiontelevision (HDTV) are also drawing near. Thus, demands are rising forlarge-capacity recording media capable of recording image informationinexpensively and simply. Although the DVD-R is to some degree securinga position as a large-capacity recording medium, it cannot be said thatthe DVD-R has a level of recording capacity adequate to satisfy futuredemands. Thus, developments are being made in optical discs for whichlaser beams having a wavelength shorter than the wavelength of laserbeams used for the DVD-R can be employed, and which discs accordinglyhave an improved recording density and a superior recording capacity.

For example, various recording and reproducing methods have beendisclosed wherein an optical information recording medium having arecording layer containing an organic dye is used to record andreproduce information by radiating onto the medium from the recordinglayer side toward the light-reflective layer side laser beams having awavelength of 530 nm or less (see, for example, Japanese PatentApplications Laid-Open (JP-A) Nos. 4-74690, 8-127174, 11-53758,11-334204, 11-334205, 11-334206, 11-334207, 2000-43423, 2000-108513,2000-113504, 2000-149320, and 2000-158818). Specifically, an informationrecording and reproducing method has been proposed for recording andreproducing information by radiating blue laser beams (wavelength: 430or 488 nm) or bluish green laser beams (wavelength: 515 nm) onto anoptical disc having a recording layer made of a dye such as a porphyrincompound, an azo dye, a metal azo dye, a quinophthalone dye, atrimethine cyanine dye, a dicyanovinylphenyl skeleton dye, or a coumalincompound.

As a result of research conducted by the inventor of the invention,however, it has been become evident that the above-mentioned opticaldiscs are deficient in terms of recording properties such as practicalsensitivity, reflectivity and degree of modulation and that furtherimprovements are accordingly required. The optical discs are alsodeficient in terms of heat and humidity stability and in terms of lightstability. Furthermore, there are also problems concerning the strength,or the film quality, of the recording film of the optical discs, andimprovements in these properties are also necessary.

For the purpose of these improvements, JP-A No. 2002-172865 discloses anoptical information recording medium having a recording layer includinga 1,2,3-triazole compound and, in order to record information into themedium, a method of radiating onto this medium laser beams having anoscillation wavelength of 405 nm. In this method, however, theperformance of optical information recording media stipulated aspreferable examples has not yet proved satisfactory.

Accordingly, dye compounds and optical information recording media arerequired which are capable of recording and reproducing information byusing laser beams having a shorter wavelength than those of laser beamsused for CD-Rs or DVD-Rs, particularly laser beams which have awavelength of 440 nm or less, and which also have excellent recordingproperties.

Dye compounds and optical information recording media are also requiredwhich are superior in terms of heat and humidity stability and in termsof light stability, and which are also satisfactory in terms of thestrength and quality of the resultant recording layers.

Further, an information recording method is required which is capable ofrecording information at a high density, using an optical informationrecording medium having a recording layer which contains a dye compoundhaving a high sensitivity to short wavelength laser beams.

SUMMARY OF THE INVENTION

As a result of eager investigation, the inventor of the invention hasdevised an optical information recording medium and an informationrecording method which have superior recording and reproducingproperties such as a high sensitivity to short wavelength laser beamshaving a wavelength of 440 nm or less, a high reflectivity and a highdegree of modulation, by using a specific recording dye (dye compound)as a recording material in a recording layer.

The inventor has also devised an optical information recording mediumwhich is superior in terms of heat and humidity stability and in termsof light stability and is also satisfactory in terms of the strength andfilm quality of the recording layer formed in the medium.

A first aspect of the invention provides an optical informationrecording medium comprising a substrate having disposed thereon arecording layer, wherein the recording layer includes a recording dyerepresented by either of the following formulae (I) and (II):

wherein A represents an aromatic ring which may have a substituent, Brepresents an aromatic ring which may have a substituent other than ahydroxyl group, n is an integer of 1 to 3, m is an integer of 2 to 6, Lrepresents either a bivalent linking group, which may have asubstituent, or a single bond, and V represents an aromatic ring, whichmay have a substituent other than L,

wherein A, B, V, n and m represent the same definitions as those of A,B, V, n and m in formula (I), respectively.

A second aspect of the invention provides a dye compound represented byeither of the following formulae (V) and (VI):

wherein R¹ and R² each independently represent a substituent, p and qare each an integer of 0 to 3, m is an integer of 2 or 3, and Vrepresents an aromatic ring, which may have a substituent,

wherein R¹, R², p, q, V and m represent the same definitions as those ofR¹, R², p, q, V and m in formula (V), respectively.

A third aspect of the invention provides a method of recordinginformation onto an optical information recording medium comprising:providing an optical information recording medium comprising a substratehaving disposed thereon a recording layer on which the information canbe recorded by radiation of a laser, the recording layer comprising arecording dye represented by the above-illustrated formula (I) or (II),providing a laser that emits light having a wavelength of 440 nm orless, and using the laser to record information on the opticalinformation recording medium. Examples of the optical informationrecording medium to which the information recording method of theinvention can be applied include the above-mentioned optical informationrecording media and optical information recording media havingembodiments described hereinafter.

The optical information recording medium and the dye compound of theinvention enable recording and reproducing information with laser beamshaving a wavelength shorter than those of laser beams used for CD-Rs orDVD-Rs, particularly laser beams having a wavelength of 440 nm or less,and further have superior recording properties. They are alsosatisfactory in terms of heat and humidity stability and in terms oflight stability. Moreover, a recording layer made of the dye issatisfactory in terms of strength and quality.

According to the information recording method of the invention, it ispossible to record information at a high density by using theabove-mentioned optical information recording medium, which has arecording layer that contains the dye compound having a high sensitivityto short wavelength laser beams.

DETAILED DESCRIPTION OF THE INVENTION

1. Optical Information Recording Medium

The optical information recording medium of the invention has asubstrate and a recording layer including a recording dye represented bythe following formula (I) or (II):

wherein A represents an aromatic ring which may have a substituent, Brepresents an aromatic ring which may have a substituent other than ahydroxyl group, n is an integer of 1 to 3, m is an integer of 2 to 6, Lrepresents a bivalent linking group, which may have a substituent, or asingle bond, and V represents an aromatic ring, which may have asubstituent other than L,

wherein A, B, V, n and m represent the same definitions as those of A,B, V, n and m in formula (I), respectively.

Examples of the aromatic ring, which may have a substituent, representedby A or B in formula (I) or (II) include hydrocarbon aromatic rings suchas benzene, naphthalene, anthracene and phenanthrene rings, and heteroaromatic rings such as pyridine, pyrimidine, quinoline, furan, pyrrole,and pyrazole rings. Preferable are benzene, naphthalene, and pyridinerings. Particularly preferable is a benzene ring.

Examples of the substituent of the aromatic ring represented by A or Bin formula (I) or (II) include chain or cyclic substituted orunsubstituted alkyl groups having 1 to 20 carbon atoms (such as methyl,ethyl, isopropyl, cyclohexyl, benzyl, phenethyl, and trifluromethylgroups), substituted or unsubstituted aryl groups having 6 to 18 carbonatoms (such as phenyl, chlorophenyl, 2,4-di-t-amylphenyl, and 1-naphthylgroups), substituted or unsubstituted alkenyl groups having 2 to 20carbon atoms (such as vinyl and 2-methylvinyl groups), substituted orunsubstituted alkynyl groups having 2 to 20 carbon atoms (such asethynyl, 2-methylethynyl, and 2-phenylethynyl groups), halogen atoms(such as F, Cl, Br and I), a cyano group, a hydroxyl group, a carboxylgroup, substituted or unsubstituted acyl groups having 2 to 20 carbonatoms (such as acetyl, benzoyl, salicyloyl, and pivaroyl groups),substituted or unsubstituted alkoxy groups having 1 to 20 carbon atoms(such as methoxy, butoxy, and cyclohexyloxy groups), substituted orunsubstituted aryloxy groups having 6 to 20 carbon atoms (such asphenoxy, 1-naphthoxy, and p-methoxyphenoxy groups), substituted orunsubstituted alkylthio groups having 1 to 20 carbon atoms (such asmethyltio, butylthio, benzylthio, and 3-methoxypropylthio groups),substituted or unsubstituted arylthio groups having 6 to 20 carbon atoms(such as phenylthio, and 4-chlorophenylthio groups), substituted orunsubstituted alkylsulfonyl groups having 1 to 20 carbon atoms (such asmethanesulfonyl, and butanesulfonyl groups), substituted orunsubstituted arylsulfonyl groups having 6 to 20 carbon atoms (such asbenzenesulfonyl, and p-toluenesulfonyl groups), substituted orunsubstituted carbamoyl groups having 1 to 17 carbon atoms (such asunsubstituted carbamoyl, methylcarbamoyl, ethylcarbamoyl,n-butylcarbamoyl, and dimethylcarbamoyl groups), substituted orunsubstituted acylamino groups having 1 to 16 carbon atoms (such asacetylamino, and benzoylamino groups), substituted or unsubstitutedacyloxy groups having 2 to 10 carbon atoms (such as acetoxy, andbenzoyloxy groups), substituted or unsubstituted alkoxycarbonyl groupshaving 2 to 10 carbon atoms (such as methoxycarbonyl, and ethoxycarbonylgroups), 5- or 6-membered, substituted or unsubstituted heterocyclicgroups (such as aromatic heterocyclic groups, for example, pyridyl,thienyl, furyl, thiazoyl, imidazoyl, and pyrazoyl groups, andnon-aromatic heterocyclic groups, for example, pyrrolidine, piperidine,morpholine, pyran, thiopyran, dioxane, and dithiolane rings).

Preferable examples of the substituent of A or B in formula (I) or (II)are chain or cyclic substituted or unsubstituted alkyl groups having 1to 16 carbon atoms, aryl groups having 6 to 14 carbon atoms, alkoxygroups having 1 to 16 carbon atoms, aryloxy groups having 6 to 14 carbonatoms, halogen atoms, a cyano group, alkoxycarbonyl groups having 2 to17 carbon atoms, carbamoyl groups having 1 to 10 carbon atoms, andacylamino groups having 1 to 10 carbon atoms.

Among these groups, more preferable examples are chain or cyclic alkylgroups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbonatoms, alkoxy groups having 1 to 10 carbon atoms, aryloxy groups having6 to 10 carbon atoms, a chlorine atom, a cyano group, alkoxycarbonylgroups having 2 to 11 carbon atoms, carbamoyl groups having 1 to 7carbon atoms, and acylamino groups having 1 to 8 carbon atoms. Amongthese groups, particularly preferable examples are chain-branched orcyclic unsubstituted alkyl groups having 1 to 8 carbon atoms,unsubstituted alkoxy groups having 1 to 8 carbon atoms, unsubstitutedalkoxycarbonyl groups having 3 to 9 carbon atoms, a cyano group, aphenyl group, and a chlorine atom.

In formal (I) or (II), the substituent of the aromatic ring representedby A or B may further have a substituent. Examples of the substituent inthis case may be the same as those described as examples of thesubstituent of the aromatic ring represented by A or B.

In formulae (I) and (II), n is an integer of 1 to 3, preferably 1 or 2,and more preferably 1.

In formulae (I) and (II), m is an integer of 2 to 6, preferably 2 to 4,and more preferably 2 or 3. In formulae (I) and (II), partial structuresdivided by parentheses [ ], the number of which is m, may be the same ordifferent.

In formula (I), L represents a bivalent linking group, which may have asubstituent, or a single bond. Examples of L include —CONR³—, —COO—,—O—, —S—, —SO—, —SO₂—, alkylene groups which may have a substituent,aryl groups which may have a substituent, and a single bond. Examples ofthe substituent which L may have are the same as those described asexamples of the substituent of the aromatic ring represented by A or Bin formula (I) or (II), and may be the partial structures included inthe parentheses [ ] in formula (I) or (II). In this case, formula (I) or(II) can be a dendrimer.

L is preferably —CONR³—, —COO— or a single bond, and more preferably—CONR³— or a single bond. R³ represents a hydrogen atom or asubstituent. R³ other than a hydrogen atom is preferably an alkyl groupwhich may have a substituent, or an aryl group which may have asubstituent. Bonding of V and L may take place in any direction.

In formulae (I) and (II), V represents an aromatic ring which may have asubstituent other than L. Examples of V include substituted orunsubstituted aryl groups having 6 to 24 carbon atoms, and 5- or6-membered substituted or unsubstituted heterocyclic groups.

In formulae (I) and (II), preferable examples of V are substituted orunsubstituted aryl groups having 6 to 18 carbon atoms, and 5- or6-membered substituted or unsubstituted heterocyclic groups. Morepreferable examples thereof are substituted or unsubstituted aryl groupshaving 6 to 18 carbon atoms.

The compound represented by formula (I) or (II) is preferably a compoundrepresented by the following formula (III) or (IV):

wherein R¹ and R² each independently represent a substituent, p and qare each an integer of 0 to 3, m is an integer of 2 to 6, L represents alinking group, which has a valence of not less than bivalence, or asingle bond, and V represents an aromatic ring, which may have asubstituent other than L,

wherein R¹, R², p, q, V and m represent the same definitions as those ofR¹, R², p, q, V and m in formula (III), respectively.

Examples and preferable examples of R¹ and R² in formulae (III) and (IV)are the same as those described as examples and preferable examples ofthe substituent of the aromatic ring represented by A or B in formula(I) or (II).

Examples and preferable examples of L and V in formulae (III) and (IV)are the same as those described as examples and preferable examples of Land V in formulae (I) and (II).

In formulae (III) and (IV), m is preferably an integer of 2 to 4, andmore preferably 2 or 3.

Each of the recording dyes represented by formulae (I) and (II), andformulae (III) and (IV), which are included as subordinate formulae informulae (I) and (II), preferably has at least one of the followingcharacteristics 1 to 4 in light of the dye being applied to therecording layer of an optical information recording medium:

-   1. The dye is preferably dissolved in an organic solvent in an    amount of 0.3 to 10% by weight of the organic solvent, and is    particularly preferably dissolved in tetrafluoropropanol in an    amount of 0.3 to 10% by weight of the tetrafluoropropanol.-   2. The melting point of the dye is 200° C. or higher, and more    preferably 300° C. or higher.-   3. The molecular weight of the dye is preferably from 300 to 2000.-   4. The pyrolysis temperature of the dye is preferably from 200 to    550° C., and more preferably from 250 to 500° C. At this time, the    weight reduction thereof is preferably 30% or more, and more    preferably 50% or more.

Preferable specific examples of the recording dye are shown below. Inthe invention, however, the dye is not limited to these examples.

Examples of Compound (Recording Dye) Represented by Formula (I):

Compound L R¹ R² 1 —NHCO— Bu(t) CH₃ 2 —NHCO— Bu(t) Bu(t) 3 —CONH— Bu(t)CH₃ 4 —COO— Bu(t) Bu(t) 5

Bu(t) CH₃ 6

H CH₃ 7

CH₃ OCH₃ 8 —NHSO₂— CH₃ CH₃ 9 —NHCONH— Bu(t) CH₃ 10 —OCO— Bu(t) Bu(t) 11—S— CH₃ CH₃ 12 —O— CH₃ CH₃ 13 —SO₂— Bu(t) CH₃ 14

Bu(t) Bu(t) 15 —CH₂CH₂— CH₃ CH₃

Examples of Compound (Recording Dye) Represented by Formula (III):

Compound R R¹ R² 21 CH₃ Bu(t) CH₃ 22 CF₃ Bu(t) CH₃ 23 CN Bu(t) CH₃ 24CO₂CH₃ Bu(t) CH₃ 25 COPh CH₃ CH₃ 26 COCH₃ CH₃ CH₃ 27 SPh Bu(t) CH₃ 28SO₂Ph Bu(t) Bu(t) 29 OCH₃ CH₃ OCH₃ 30 N(CH₃)₂ H CH₃

Examples of Compound (Recording Dye) Represented by Formula (II) or(IV):

Compound R X 35 CO₂CH₂CH₃ CH 36 COPh CH 37 SPh CH 38 CN CH 39 Cl N 40CF₃ CH

The optical information recording medium of the invention has, on asubstrate, a recording layer including a recording dye represented byformula (I) or (II). The optical information recording medium of theinvention may have various structures, and preferably has a structure inwhich the recording layer, a light-reflective layer and a protectivelayer are disposed in that order on a disc-shaped substrate having apre-groove at a constant track pitch, or a structure in which alight-reflective layer, the recording layer, and a protective layer aredisposed in that order on the disc-shaped substrate. Moreover, anotherpreferable structure of the optical information recording medium is astructure in which two laminates each having the recording layer and alight-reflective layer on a disc-shaped transparent substrate having apre-groove at a constant track pitch are jointed to each other so thatthe two recording layers are disposed inward.

In order to attain a higher recording density, a substrate on which apre-groove having a narrower track pitch than that of a pre-groove ofCD-Rs or DVD-Rs is made can be used in the optical information recordingmedium of the invention. In the optical information recording medium ofthe invention, the track pitch is preferably from 0.2 to 0.8 μm, morepreferably from 0.25 to 0.6 μm, and even more preferably from 0.27 to0.4 μm.

The depth of the pre-groove is preferably from 0.03 to 0.18 μm, morepreferably from 0.05 to 0.15 μm, and even more preferably from 0.06 to0.1 μm.

A process for producing the optical information recording medium of theinvention will be explained hereinafter by way of a medium having, on adisc-shaped substrate, a recording layer, a light-reflective layer and aprotective layer in that order.

The substrate of the optical information recording medium of theinvention can be made of any material that is used as a material for thesubstrate of a conventional optical information recording medium.Examples of the material for the substrate include glass, polycarbonate,acrylic resins such as polymethyl methacrylate, vinyl chloride resinssuch as polyvinyl chloride and polyvinyl chloride copolymers, epoxyresins, amorphous polyolefins, and polyesters. If necessary, thesematerials may be used in combination. These materials can be used in theform of a film or a rigid substrate. Among the above-mentionedmaterials, polycarbonate is preferable from the viewpoints of moistureresistance, dimensional stability, and costs.

An undercoat layer may be provided on the substrate surface on which arecording layer is to be formed, in order to improve flatness of thesubstrate and adhesive strength between the substrate and the recordinglayer and prevent deterioration of the recording layer. Examples of thematerial for the undercoat layer include polymer materials such aspolymethyl methacrylate, acrylic acid/methacrylic acid copolymers,styrene/maleic anhydride copolymers, polyvinyl alcohol,N-methylolacrylamide, styrene/vinyltoluene copolymers, chlorosulfonatedpolyethylene, nitrocellulose, polyvinyl chloride, chlorinatedpolyolefins, polyesters, polyimides, vinyl acetate/vinyl chloridecopolymers, ethylene/vinyl acetate copolymers, polyethylene,polypropylene, and polycarbonate; and surface-modifiers such as silanecoupling agents. The undercoat layer can be formed by dissolving ordispersing the above-mentioned material in a suitable solvent to preparea coating solution, and then applying this coating solution onto thesurface of the substrate by a coating method such as a spin coatingmethod, a dip coating method, or an extrusion coating method. Thethickness of the undercoat layer is generally from 0.005 to 20 μm, andpreferably from 0.01 to 10 μm.

The recording layer can be formed by dissolving the above-mentionedrecording dye, and, if necessary, a quencher, and a binder in a solventto prepare a coating solution, applying this coating solution onto thesurface of the substrate to form a coating film, and then drying thecoating film.

Examples of the solvent in the coating solution include esters such asbutyl acetate, ethyl lactate, and cellosolve acetate; ketones such asmethyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone;chlorinated hydrocarbons such as dichloromethane, 1,2-dichloroethane,and chloroform; amides such as dimethylformamide; hydrocarbons such asmethylcyclohexane; ethers such as dibutyl ether, diethyl ether,tetrahydrofuran, and dioxane; alcohols such as ethanol, n-propanol,isopropanol, n-butanol, and diacetone alcohol; fluorine-containingsolvents such as 2,2,3,3-tetrafluoropropanol; and glycol ethers such asethylene glycol monomethyl ether, ethylene glycol monoethyl ether, andpropylene glycol monomethyl ether. These solvents can be used alone orin combination in consideration of solubility of the dye used.Furthermore, the coating solution may contain various additives such asan antioxidant, a UV absorbent, a plasticizer and a lubricant, ifnecessary.

When the binder is used, examples thereof include natural organicpolymer materials such as gelatin, cellulose derivatives, dextran,rosin, and rubber; and synthetic organic polymers such as hydrocarbonresins including polyethylene, polypropylene, polystyrene, andpolyisobutylene, vinyl resins including polyvinyl chloride,polyvinylidene chloride, and vinyl chloride/vinyl acetate copolymers,acrylic resins including polymethyl acrylate, and polymethylmethacrylate, polyvinyl alcohol, chlorinated polyethylene, epoxy resin,butyral resin, rubber derivatives, and initially-condensed products ofthermoplastic resins including phenol/formaldehyde resins. When thebinder is used as one of the materials of the recording layer, theamount (mass) of the binder used is generally from 0.01 to 50 times, andpreferably from 0.1 to 5 times as many as the mass of the recording dye.The concentration of the recording dye in the coating solution isgenerally from 0.01 to 10% by mass, and preferably from 0.1 to 5% bymass.

Examples of the coating method of the coating solution include spray,spin coating, dipping, roll coating, blade coating, and doctor rollmethods, and a screen printing method. The recording layer may bemonolayered or multilayered. The thickness of the recording layer isgenerally from 20 to 500 nm, preferably from 30 to 300 nm, and morepreferably from 50 to 100 nm.

The recording layer may contain any anti-color fading agent in order toimprove light fastness of the recording layer. As the anti-color fadingagent, a singlet oxygen quencher is generally used. As the singletoxygen quencher, those described in known publications such as patentspecifications can be used.

Specific examples thereof include singlet oxygen quenchers described inJP-A Nos. 58-175693, 59-81194, 60-18387, 60-19586, 60-19587, 60-35054,60-36190, 60-36191, 60-44554, 60-44555, 60-44389, 60-44390, 60-54892,60-47069, 63-209995, and 4-25492, and Japanese Patent ApplicationPublication (JP-B) Nos. 1-38680 and 6-26028, German Patent No. 350399,and the Journal of the Chemical Society of Japan, 1992, October, p.1141. A preferable example of the singlet oxygen quencher is a compoundrepresented by the following formula (VII):

wherein R²¹ represents an alkyl group which may have a substituent, andQ⁻ represents an anion.

In formula (VII), R²¹ is generally an alkyl group which may have asubstituent and has 1 to 8 carbon atoms, and is preferably anunsubstituted alkyl group having 1 to 6 carbon atoms. Examples of thesubstituent of the substituted alkyl group include halogen atoms (suchas F or Cl), alkoxy groups (such as methoxy and ethoxy groups),alkylthio groups (such as methylthio and ethylthio groups), acyl groups(such as acetyl and propionyl groups), acyloxy groups (such as acetoxyand propionyloxy groups), a hydroxy group, alkoxycarbonyl groups (suchas methoxycarbonyl and ethoxycarbonyl groups), alkenyl groups (such as avinyl group), and aryl groups (such as phenyl and naphthyl groups).Among these substituents, halogen atoms, alkoxy groups, alkylthio groupsand alkoxycarbonyl groups are preferable. Preferable examples of theanion of Q⁻ include ClO₄ ⁻, AsF₆ ⁻, BF₄ ⁻ and SbF₆ ⁻.

Examples of the compound represented by formula (VII) are shown in thefollowing Table 1.

TABLE 1 Compound No. R²¹ Q⁻ VII-1 CH₃ ClO₄ ⁻ VII-2 C₂H₅ ClO₄ ⁻ VII-3n-C₃H₇ ClO₄ ⁻ VII-4 n-C₄H₉ ClO₄ ⁻ VII-5 n-C₅H₁₁ ClO₄ ⁻ VII-6 n-C₄H₉ SbF₆⁻ VII-7 n-C₄H₉ BF₄ ⁻ VII-8 n-C₄H₉ AsF₆ ⁻

The use amount of the anti-color fading agent such as the singlet oxygenquencher is usually from 0.1 to 50% by mass, preferably from 0.5 to 45%by mass, more preferably from 3 to 40% by mass, and even more preferablyfrom 5 to 25% by mass of the recording dye.

It is preferred to form a light-reflective layer adjacently to therecording layer in order to improve reflectivity of the recording mediumat the time of reproducing information. The material of thelight-reflective layer is a light-reflective material, which is amaterial having a high reflectivity to laser beams. Examples thereofinclude metals and semi-metals, such as Mg, Se, Y, Ti, Zr, Hf, V, Nb,Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn,Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn and Bi; and stainless steel.These materials may be used alone, or in combination, or may be used inthe form of alloy. Among these examples, preferable are Cr, Ni, Pt, Cu,Ag, Au, Al and stainless steel. Particularly preferable are Au, Ag andAl metals, and alloys thereof. The most preferable are Ag and Al metals,and alloys thereof. The light-reflective layer can be formed on thesubstrate or the recording layer, for example, by vapor-depositing,sputtering or ion-plating the light-reflective material. The thicknessof the light-reflective layer is generally from 10 to 300 nm, andpreferably from 50 to 200 nm.

It is preferable to form, on the light-reflective layer or the recordinglayer, a protective layer in order to physically and chemically protectthe recording layer or the like. When the optical information recordingmedium has the same structure as that of DVD-R type optical informationrecording media, that is, when the medium has a structure in which twosubstrates are bonded to each other so that their recording layers aredisposed inward, it is unnecessary to form the protective layer.Examples of the material used in the protective layer include inorganicmaterials such as SiO, SiO₂, MgF₂, SnO₂, and Si₃N₄; and organicmaterials such as thermoplastic resins, thermosetting resins and UVcurable resins. The protective layer can be formed, for example, bylaminating on the reflective layer a film (transparent sheet) obtainedby extruding a plastic with an adhesive agent, or by vacuum-evaporating,sputtering, or applying the protective layer material. When theprotective layer is made of the thermoplastic resin or the thermosettingresin, the protective layer can be formed by dissolving the resin in asuitable solvent to prepare a coating solution, applying this coatingsolution to the recording layer or the light-reflective layer, and thendrying the applied layer. When the protective layer is made of the UVcurable resin, the protective layer can be formed by applying the resinas it is or applying a coating solution prepared by dissolving the resinin a suitable solvent, and then radiating UV light onto the appliedlayer so as to cure the resin. The coating solution may contain variousadditives such as an antistatic agent, an antioxidant, and a UVabsorbent, if necessary. In general, the thickness of the protectivelayer (or the thickness of the transparent sheet if the sheet is used asthe protective layer) is preferably from 0.1 μm to 1 mm.

Since the optical information recording medium of the invention includesthe above-mentioned recording dye in the recording layer thereof, themedium has a high refractive index to light having a wavelength of 440nm or less. Dependently on the recording dye used, the absorptioncoefficient of the medium can be high or low in a suitable wavelengthrange. As a result, the optical information recording medium can exhibita high sensitivity to short wavelength laser beams having a wavelengthof 440 nm or less, and can have a high reflectivity and a high degree ofmodulation thereto. Since the above-mentioned recording dye has highfastness, the recording medium is excellent in terms of moisture andheat resistance and light stability and further the recording layer madeof the dye is satisfactory in terms of strength and film quality.

2. Dye Compound

The dye compound of the invention is represented by the followingformula (V) or the following formula (VI):

wherein R¹ and R² each independently represent a substituent, p and qare each an integer of 0 to 3, m is an integer of 2 or 3, and Vrepresents an aromatic ring, which may have a substituent,

wherein R¹, R², p, q, V and m represent the same definitions as those ofR¹, R², p, q, V and m in formula (V), respectively.

In the dye compound of the invention, examples of R¹, R², p, q, V and mare the same as those described in the explanations for theabove-mentioned recording dye. Examples of the dye compound are also thesame as those described in the explanations for the recording dye.

The dye compound can be applied to any optical information recordingmedium including a dye recording layer since the dye compound issuperior in fastness. Since the dye compound has a high refractive indexto light having a wavelength of 440 nm or less, it is preferred to applythe dye compound to the recording dye of the optical informationrecording medium of the invention.

The method for producing the dye compound of the invention will bedescribed in Synthesis Examples described later.

3. Information Recording Method

In the information recording method of the invention, information isrecorded onto an optical information recording medium having, on asubstrate, a recording layer on which the information can be recorded byradiating thereto laser beams having a wavelength of 440 nm or less andwhich includes the above-mentioned recording dye.

Specifically, the method can be performed by using the opticalinformation recording medium of the invention as follows.

While the optical information recording medium is rotated at a constantlinear velocity or a constant angular velocity, recording light such assemiconductor laser beams is first radiated onto the medium from thesubstrate side or the protective layer side. Then, the recording layerabsorbs the light, so that the temperature of the recording layer riseslocally. As a result, a physical or chemical property of the irradiatedportions of the recording layer changes (for example, pits aregenerated), so that the optical property of the recording layer locallychanges. Thus, information is recorded on the medium. In the invention,as a source of the recording light, a semiconductor laser having anoscillation wavelength ranging from 390 to 450 nm may be used.Preferable examples of the light source include bluish purplelight-emitting semiconductor lasers having an oscillation wavelengthranging from 390 to 415 nm, and bluish purple light-emitting SHG lasershaving a central oscillation wavelength of 425 nm, in which SHG lasersan optical waveguide element is used to reduce the central oscillationwavelength (850 nm) of infrared semiconductor lasers to half. Amongthese, the bluish purple light-emitting semiconductor lasers areparticularly preferable since a high recording density can be attained.The information recorded as described above can be reproduced byradiating semiconductor laser beams onto the optical informationrecording medium from the substrate side or the protective layer sidewhile the medium is rotated at the same linear velocity as thatdescribed above, and detecting light reflected by the medium.

EXAMPLES

The present invention will be described in more detail by way of thefollowing examples. However, the invention is not limited to theexamples.

Synthesis Example 1

Synthesis of Compound 1 Exemplified as Recording Dye

0.33 g of5-carboxy-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazole wasdissolved in 20 ml of methylene chloride. 0.1 ml of oxazolyl chloridewas added to the resultant solution. The resulting solution was stirredat room temperature for 1 hour, and then 54 mg of phenylenediamine and0.3 ml of triethylamine were added to the solution. The resultantsolution was stirred for 2 hours, and then water was added to thesolution, so as to extract the organic material with methylene chloride.This methylene chloride solution was dried with sodium sulfate and thenthe solvent of the solution was distilled off. The remaining solid waswashed with ethyl acetate and 0.3 g of compound 1 was obtained.

λmax=361 nm (CHCl₃) Mass (posi)=722

Synthesis Example 2

Synthesis of Compound 21 Exemplified as Recording Dye

Five milliliter of an aqueous solution in which 0.5 g of sodiumcarbonate was dissolved in 5 ml of toluene was added to 0.5 g of4-bromo-6-methyl-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazol,0.18 g of pinacol ester of benzene-1,3,5-triboric acid, and 15 mg ofpalladium acetate. 27 mg of tri-tert-butylphosphine was added to theresultant solution while the solution was stirred under nitrogen flow.The resultant solution was stirred at 80° C. for 10 hours, and then 1 Nhydrochloric acid was added thereto. After the resultant mixtureseparated into two phases, the aqueous phase was removed. The remainingorganic phase was dried with sodium sulfate and the solvent in theorganic phase was distilled off. The remaining solid was purified withsilica gel chromatography and 0.3 g of compound 21 was obtained.

λmax=349 nm (CHCl₃) Mass (posi)=958

Synthesis Example 3

Synthesis of Compound 40 Exemplified as Recording Dye

Five milliliter of an aqueous solution in which 0.5 g of sodiumcarbonate was dissolved in 5 ml of toluene was added to 0.6 g of pinacolester of5-tert-butyl-3-(5-trifluoromethyl-2H-benzotriazolyl)-2-hydroxyphenylboricacid, 0.18 g of 1,3,5-triiodobenzene and 15 mg of palladium acetate. 27mg of tri-tert-butylphosphine was added to the resultant solution whilethe solution was stirred under nitrogen flow. The resultant solution wasstirred at 80° C. for 10 hours, and then 1 N hydrochloric acid was addedthereto. After the resultant mixture separated into two phases, theaqueous phase was removed. The remaining organic phase was dried withsodium sulfate and the solvent in the organic phase was distilled off.The remaining solid was purified with silica gel chromatography and 0.2g of compound 40 was obtained.

λmax=359 nm (CHCl₃) Mass (posi)=1078

Synthesis Examples of the above-mentioned recording dyes (dye compounds)are mere examples, and the recording dyes applied to the invention(i.e., the recording dyes represented by formulae (I) to (IV)) can beprepared by modifying the Synthesis Examples in various ways.

Example 1

Compound 1 exemplified as the recording dye was dissolved inmethylcyclohexane to yield a recording layer coating solution(concentration: 1% by mass). A polycarbonate substrate (diameter: 120mm, thickness: 0.6 mm) on the surface of which a spiral pre-groove(track pitch: 0.4 μm, groove width: 0.2 μm, and groove depth: 0.08 μm)was formed by injection molding was prepared. The coating solution wasapplied onto the pre-groove-formed surface of the substrate by spincoating so as to form a recording layer (thickness thereof in thepre-groove: about 80 nm).

Next, silver was sputtered onto the recording layer to form alight-reflective layer having a thickness of about 100 nm. Furthermore,a UV curable resin (SD 318 manufactured by Dainippon & Ink Chemicals,Inc.) was applied onto the light-reflective layer. Then, the appliedresin was exposed to ultraviolet rays so as to cure the resin, therebyforming a protective layer having a thickness of 7 μm.

An optical information recording medium of the invention was thusobtained.

Examples 2 to 8

Optical information recording media of the invention were produced inthe same way as in Example 1 except that compound 1 was changed tocompounds shown in Table 2 (without changing the amount thereof).

Comparative Examples 1 to 5

Optical information recording media for comparison were produced in thesame way as in Example 1 except that compound 1 was changed tocomparative dye compounds A to E (without changing the amount thereof)and the solvent of the coating solution was changed to2,2,3,3-tetrafluoropropanol.

The comparative dye compounds A to E are shown bellow.

Comparative Compounds

(A) Compound Described in Example 1 of JP-A No. 4-74690

(B) Compound (III) Described in Example 1 of JP-A No. 11-334205

(C) Specific Example (14) Described in JP-A No. 2002-172865

(D) Specific Example (15) Described in Examples of JP-A No. 2002-172865

(E) Specific Example (18) Described in JP-A No. 2002-163799

Evaluation of Optical Information Recording Media

A semiconductor laser having an oscillation wavelength of 405 nm andemitting bluish purple light was used to record 14T-EFM signals ontoeach of the produced optical information recording media at a linearvelocity of 3.5 m/second. Thereafter, the recorded signals werereproduced.

The degree of modulation of each medium, reflectivity of thenon-recorded portions of each medium, and sensitivity of each mediumwere measured at an optimal power. Light from a xenon light sourcehaving an illuminance of 100,000 lux was radiated onto each of theoptical discs for 3 days without using any UV filter. Thereafter,reflectivity of the non-recorded portions of each medium was measured. ADDU 1000 (trade name) manufactured by Pulstec Industrial Co., Ltd. wasused to perform recording and evaluation of recording properties of themedia. The evaluation results are shown in the following Table 2.

TABLE 2 Dye Reflectivity Modula- Reflectivity (%) compound in (%) ofnon- tion Sensi- of non-recorded recording recorded degree tivityportions (after layer portions (%) (mW) light radiation) Example 1  (1)72 62 6.1 72 Example 2  (6) 69 58 6.2 69 Example 3 (18) 68 63 7.2 68Example 4 (20) 74 64 6.4 74 Example 5 (21) 70 68 6.7 70 Example 6 (23)70 68 5.2 70 Example 7 (35) 71 65 6.3 71 Example 8 (37) 63 66 5.6 62Comparative (A) 35 58 7.9 0 Example 1 Comparative (B) 36 41 9.7 0Example 2 Comparative (C) 66 58 7.3 0 Example 3 Comparative (D) 73 656.5 55 Example 4 Comparative (E) No signals were able to be recordedExample 5 since the recording layer whitened.

It can be understood from the results shown in Table 2 that the opticaldiscs of the invention (Examples 1 to 8) exhibits a higher reflectivityto the bluish purple semiconductor laser beams and have a higher degreeof modulation and a higher sensitivity thereto than the optical discshaving the recording layers which contained the comparative compounds Ato E, respectively.

Accordingly, it has been understood that optical discs having highrecording properties to short wavelength laser beams can be obtained byusing the recording dyes of the invention. It has also been confirmedthat recording layers made of the recording dye have sufficient strengthand high light fastness.

1. An optical information recording medium comprising: a disc-shapedsubstrate, a surface of which has a pre-groove having a track pitch of0.2 to 0.8 μm; and a recording layer comprising a recording dyerepresented by either of the following formulae (V) or (VI) on thesurface of the substrate having the pre-groove:

wherein R¹ and R² each independently represent a substituent, p and qare each an integer of 0 to 3, m represents a number of valence bondsbetween 2 to 4, and when m=2 V is selected from the group consisting ofa 2,3-naphthylene group, a 1,5-naphthylene group, a 3,4-thiophenylenegroup, a 5,6-benzthiazolylene group, and a 2,6-pyridinylene group eachof which may have a substituent; when m=3 V is selected from the groupconsisting of a benzene-1,3,5-triyl group and a 2,4,6-pyridinylene groupeach of which may have a substituent; and when m=4 V is abenzene-1,2,4,5-tetrayl group which may have a substituent,

wherein R¹, R², p, q, V and m represent the same definitions as those ofR¹, R², p, q, V and m in formula (V), respectively.
 2. The opticalinformation recording medium of claim 1, wherein in both formulae (V)and (VI), V represents a benzene-1,3,5-triyl group, abenzene-1,2,4,5-tetrayl group or a 2,4,6-pyridinylene group, which mayhave a substituent, respectively.
 3. The optical information recordingmedium of claim 1, wherein in both formulae (V) and (VI), m representsan integer of 3 and V represents a benzene-1,3,5-triyl group or a2,4,6-pyridinylene group, which may have a substituent, respectively. 4.The optical information recording medium of claim 1, further comprisinga light-reflective layer made of a metal, between the recording layerand the surface of the substrate having the pre-groove.
 5. The opticalinformation recording medium of claim 4, further comprising a protectivelayer on the recording layer.
 6. A method for recording information ontoan optical information recording medium, the optical informationrecording medium comprising: a disc-shaped substrate, a surface of whichhas a pre-groove having a track pitch of 0.2 to 0.8 μm; and a recordinglayer comprising a recording dye represented by either of the followingformulae (V) or (VI) on the surface of the substrate having thepre-groove:

wherein R¹ and R² each independently represent a substituent, p and qare each an integer of 0 to 3, m represents a number of valence bondsbetween 2 to 4, and when m=2 V is selected from the group consisting ofa 2,3-naphthylene group, a 1,5-naphthylene group, a 3,4-thiophenylenegroup, a 5,6-benzthiazolylene group, and a 2,6-pyridinylene group eachof which may have a substituent; when m=3 V is selected from the groupconsisting of a benzene-1,3,5-triyl group and a 2,4,6-pyridinylene groupeach of which may have a substituent; and when m=4 V is abenzene-1,2,4,5-tetrayl group which may have a substituent,

wherein R¹, R², p, q, V and m represent the same definitions as those ofR¹, R², p, q, V and m in formula (V), respectively, the methodcomprising: providing a laser that emits light having a wavelength equalto or less than 440 nm, and using the laser to record information on theoptical information recording medium.
 7. The information recordingmethod of claim 6, wherein the optical information recording mediumfurther comprises a light-reflective layer made of a metal, between therecording layer and the surface of the substrate having the pre-groove.8. The information recording method of claim 7, wherein the opticalinformation recording medium further comprises a protective layer on therecording layer.
 9. The information recording method of claim 8, whereinthe laser emits light having a wavelength of 405 nm.
 10. A dye compoundrepresented by either of the following formulae (V) or (VI):

wherein R¹ and R² each independently represent a substituent, p and qare each an integer of 0 to 3, m represents a number of valence bondsbetween 2 to 4, and when m=2 V is selected from the group consisting ofa 2,3-naphthylene group, a 1,5-naphthylene group, a 3,4-thiophenylenegroup, a 5,6-benzthiazolylene group, and a 2,6-pyridinylene group eachof which may have a substituent; when m=3 V is selected from the groupconsisting of a benzene-1,3,5-triyl group and a 2,4,6-pyridinylene groupeach of which may have a substituent; and when m=4 V is abenzene-1,2,4,5-tetrayl group which may have a substituent,

wherein R¹, R², p, q, V and m represent the same definitions as those ofR¹, R², p, q, V and m in formula (V), respectively.
 11. The dye of claim10, wherein in both formulae (V) and (VI), m represents a number ofvalence-bond and V represents an aromatic ring selected from the groupconsisting of a benzene-1,3,5-triyl group, a benzene-1,2,4,5-tetraylgroup, and a 2,4,6-pyridinylene group, which may have a substituent. 12.The dye of claim 10, wherein in both formulae (V) and (VI), m representsan integer of 3 and V represents an aromatic ring selected from thegroup consisting of a benzene-1,3,5-triyl group and a 2,4,6-pyridinylenegroup, which may have a substituent.
 13. The dye of claim 12, whereinthe dye is selected from the group consisting of the following Compounds21 to 30 and 35 to 40:

Compound R R¹ R² 21 CH₃ Bu(t) CH₃ 22 CF₃ Bu(t) CH₃ 23 CN Bu(t) CH₃ 24CO₂CH₃ Bu(t) CH₃ 25 COPh CH₃ CH₃ 26 COCH₃ CH₃ CH₃ 27 SPh Bu(t) CH₃ 28SO₂Ph Bu(t) Bu(t) 29 OCH₃ CH₃ OCH₃ 30 N(CH₃)₂ H CH₃

Compound R X 35 CO_(z)CH_(z)CH₃ CH 36 COPh CH 37 SPh CH 39 Cl N 40 CF₃CH.